This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. To determine the role of fibroblasts heterogeneity in the pathogenesis of Graves'ophthalmopathy (GO). GO is an autoimmune process associated with lymphocyte and mast cell recruitment resulting in hyaluronan deposition and inflammation of the orbit. This laboratory has demonstrated that orbital fibroblasts exhibit phenotypic attributes that distinguish them from other fibroblasts. The hypothesis to be tested in this proposal is that exaggerated responses of the orbital fibroblasts to pro-inflammatory cytokines and CD40 activation by its ligand (CD40L) in fibroblasts subsets represent the molecular basis of GO. Populations of orbital fibroblasts subsetted according to Thy-1 expression or its absence both display surfact CD40 but exhibit distinct metabolic characteristics. Moreover, CD40 activation by CD40L enhances IL-6 and IL-8 expression. Data presented in this application support the concept that CD40 expression represents a major signal conduit for orbital fibroblasts activation by T lymphocytes and mast cells.